The present invention relates to the use of snake venom as an analgesic.
Although pain is a crucially important physiological response, it also results in unnecessary suffering and agony. The control and relief of pain is an important branch of medicine. Pain may come about both as a result of disease as well as a result of medical treatment such as chemotherapy. In either case, it is important to alleviate the pain as much as possible so as to enable the sufferer to function normally.
Two neural pathways relating to pain act concurrently in the body: (1) a sensory pathway which senses tissue damage and subsequently produces a feeling of pain; (2) an analgesic pathway which reduces the feeling of pain and prevents the flow of information about the pain to the central nervous system (CNS), thus allowing the organism to maintain it""s normal activity in spite of an injury. Anesthesia can be realized either by use of a drug which inhibits peripheral nerves that act as pain sensors or by enhancement of the natural analgesic system. Since these are different pathways, they are affected by different substances. For example, aspirin and lidocaine are active on the peripheral sensory pathway, while morphine and related substances are active on the analgesic system.
The most efficient analgesics currently in use are morphine-related substances of opiatic origin. It""s well known that the brain makes a variety of endogenic opiates, and this explains the powerful effect of these substances. Their action on neurons is mediated by specialized receptors. Signals regulated by these receptors prevent the flow of information from the peripheral pain neurons to the CNS. These CNS neurons are also sensitive to a variety of other chemical substances including catecholamines (serotonin, noradrenalin etc.), neuroactive peptides (neurotensin) and inhibitory amino acids (glycin and GABA).
Out of some 4000 currently living species of snakes, approximately 400 species are known to be venomous. The venomous species are classified into five families, one of which is the Viperidae family, commonly known as vipers. Snakes of the Viperidae are distributed in Europe, Asia and Africa, and comprise 8 genera, one of which is the genus Vipera. The genus Vipera comprises the following species: V. berus; V. lebatina; V. russelii; V. superciliaris; V. ursinii; V. aspis; V. latifii; V. bornmulleri; V. ammodytes; V. xanthina; and V. mauritanica. The species V. xanthina has been further classified into three sub-species: V. xanthina raddei, V. xanthina xanthina, which is found generally in southern Europe, and V. xanthina palestinae which is found in Israel.
Snake venom comprises a large variety of different substances. Out of several hundreds of estimated compounds, it is believed that only 4-8 are involved in the toxic effect of the venom. Despite functional similarity, snake venoms differ considerably in their chemical composition. Each species possesses it""s own characteristic venom composition. To date, only a few hundred compounds from some 400 venomous snake species have been characterized. These include enzymes, toxins, growth factors, etc. Most of the isolated venom compounds are of unknown function.
Traditionally, snake venom is considered a source of toxic substances. However, it is also a source of analgesics. Doctors who treated patients bitten by a South American snake (Crotalus durissus terrificus) reported that although these patients were in a life-threatening condition, they felt no pain. A neurotoxin product isolated from snake venom was regarded as a new type of analgesic at the First Congress of Neurotoxicology (1977) in Yugoslavia. These and other observations lead to attempts to isolate anesthetic compounds from snake venom.
Bevan, P. and Hiestand, P. (1983) J. Biol. Chem. 258:5319-5326 describe a single chain polypeptide isolated from Vipera russelli russelli venom by cation exchange chromatography. The polypeptide competes with the binding of monoamines and opiate ligands to their respective receptors, and injection of the polypeptide intracerebroventricularly in rats causes marked sedation. The authors state that the polypeptide is a large and highly charged molecule which is unlikely to pass the blood-brain barrier. The polypeptide was found to be a moderately potent toxin, similar to the crude venom.
Dutta, A. S. and Chaudhuri, A. K. N. (1991) Indian J. Exp. Biol. 29:937-942 describe experiments carried out with crude venom of Vipera russelli on mice and rats. The venom was injected intraperitoneally and intravenously, and was found to produce alterations in general behavior patterns connected with the CNS. The venom showed significant analgesic activity in one assay, but no activity in two other assays.
WO 91/01740 published Feb. 21, 1991 discloses the use of lyophilized Crotalus atrox whole venom in a pharmaceutical composition for external use. The composition has analgesic, hyperaemizating and spasmolysant activity.
Giorgi, R., Bernardi, M. M. and Cury, Y. (1993) Toxicon 31:1257-1265 describe analgesic effects evoked by low molecular weight substances extracted from Crotalus durissus terrificus venom by ultrafiltration. The extract was administered to mice subcutaneously, intraperitoneally and orally.
CN 1,072,344 published May 26, 1993 discloses a snake toxin ointment containing a commercial snake toxin enzyme (source not given), a leukocyte peptide factor and Bingpian, a known Chinese analgesic medicine. The ointment functions as an antibiotic with no toxicity or side effects.
Pu, X. C., Wong, P. T. H. and Gopalakrishnakone, P. (1995) Toxicon 33:1425-1431 describes a neurotoxin purified from king cobra venom by gel filtration and HPLC. The toxin was administered i.p., p.o. or i.c.v. to mice and found to have a potent analgesic effect.
U.S.S.R. Patent No. 435,824 describes an analgesic composition prepared from Nayaksin dry cobra venom. This snake is from the Naja species which belongs to the Elapidae family.
For over 20 years, an ointment named Viprosalum or Viprosal has been available in the former Soviet Union and in Eastern Europe for the relief of pain. This ointment is a mixture of a viper venom (European species) dissolved in Vaseline together with Lanolin, camphor and solicilate.
It is an object of the present invention to provide an analgesic substance isolated from snake venom which is substantially non-toxic.
According to one aspect of the present invention, there is provided a substantially non-toxic fraction isolated from the venom of Vipera xanthina, the fraction having an analgesic effect.
Further in accordance with this aspect of the present invention, there is provided a pharmaceutical composition for use as an analgesic comprising a substantially non-toxic fraction isolated from the venom of Vipera xanthina. 
In a preferred embodiment of the present invention, the pharmaceutical composition is for topical use.
Although all of the experiments described below which illustrate the invention involve the sub-species Vipera xanthina palestinae (hereinafter V. palestinae). It is to be understood that this sub-species serves only as an example for the entire species Vipera xanthina. As stated above, each venomous species possesses it""s own characteristic venom composition.
The fraction provided by the invention combines a number of properties previously unreported as appearing together in the same material. These properties include: (1) derivation from Vipera xanthina venom; (2) possession of analgesic activity; (3) substantially no toxicity; (4) substantially purified; and (5) active when administered topically. This substance has been named xe2x80x9cZephalinxe2x80x9d.
In the present specification, the term non-toxic is defined as the non-occurrence of pathological phenomena as a result of using pharmacological levels of Zephalin which have an analgesic effect. The term substantially non-toxic is defined as including acceptably low toxicity as well as non-toxicity.
Although Zephalin is a purified fraction of the crude venom, it apparently comprises more than one substance. The present invention includes not only Zephalin but also various products which may be purified from Zephalin and which possess the properties of Zephalin. The invention also includes derivatives of these products, which retain the properties of Zephalin. In the case of proteinaceous material, such derivatives would include proteins or polypeptides in which one or more amino acids have been added, deleted and/or replaced. Other chemical modifications are also contemplated.
Zephalin may be used to prepare a pharmaceutical composition for use as an analgesic. Such a composition would also comprise a pharmaceutically acceptable carrier or excipient such as a mixture of Lanolin and Vaseline. The composition may be prepared for parenteral use, for example in a saline solution, or for topical use in an ointment, cream or salve. In order to afford relief to a subject suffering from pain, the pharmaceutical composition would either be injected or applied topically at an appropriate location. Other possible modes of application would be oral and rectal. Any pharmaceutical composition would generally include a pharmaceutically acceptable carrier or excipient in addition to the active ingredient. As Zephalin sometimes acts after a lag period, it is to be expected that it will be especially effective with respect to chronic pain, although it may be used to treat any type of pain.